The present invention relates to an ignition control apparatus for an engine which is particularly suitable -or controlling ignition timings of a marine engine.
FIG. 4 shows a circuit diagram of a conventional ignition control apparatus for a marine engine. The conventional ignition control apparatus illustrated includes a generator coil 101 of a magneto generator which generates an alternating current output in synchrony with the rotation of an engine, a rectifier diode 102 for rectifying the alternating current output of the generator coil 101, a capacitor 103 which is charged by the output of the generator coil 101 through the rectifier diode 102, an ignition coil 104 having a primary winding connected to the capacitor 103 and a secondary winding, a spark plug 105 connected to the secondary winding of the ignition coil 104 so as to generate a spark when a high voltage develops across the secondary winding, a thyrister 106 for controlling the ignition coil 104, &he thyrister 106 having an anode connected to a junction between the rectifier diode 102 and the capacitor 103, a cathode connected to ground and a control gate for controlling the conduction of the thyrister 106, and a pick-up coil 107 connected to the control gate of the thyrister 106 through a rectifier diode 108 and a resistor 109 for periodically generating an ignition signal at a predetermined piston position of a cylinder in synchrony with the rotation of the engine so as to control the thyrister 106.
In operation, as the engine operates, the generator coil 101 generates an alternating current output which, after being rectified by a rectifier diode, is supplied to the capacitor 103 so as to charge it. When the thyrister 106 is made conductive by an ignition signal which is generated by the pick-up coil 107 and supplied to the control gate of the thyrister 106, the charged capacitor 103 discharges through the now conductive thyrister 106 so that a high voltage is developed on the secondary winding of the ignition coil 104, causing the spark plug 105 to electrically spark.
With the conventional ignition control apparatus for a marine engine as described above, the thyrister 106 is directly controlled by the output signal of the pick-up coil 107 alone, and no means is provided for calculating and controlling optimal ignition timings on the basis of the operating condition of the marine engine. Thus, it is impossible to change the ignition timing in accordance with the operating condition of the marine engine, so it is difficult to concurrently control both the startability and the idling property during the trolling (low-speed) operation of the engine in a proper manner.